Regarding the 6MT, It is definitely not archaic. It is very similar to the E92 transmission (may be the same one?). The gears are definitely closer together from a shifting standpoint - and by using the term notchy I mean you can really "feel" the gear reach it's way into place. Half of that feeling is probably due to it being brand new and will become more smooth with time.
The ratios are very well calculated as well - I actually have a first gear again! At least compared to the M3 I would only use first to get the car rolling from 0-3mph then get to second. In the 335i you actually need first for the first 7-10mph and you can comfortably shift out from 20mph if you need some pull asap. The shifts are fast and the clutch is quite nice. I did the CDV delete (clutch delay valve) on my E92 335i and the 6MT F30 335i feels similar to a CDV-deleted E92 335i. I am not sure if this model even has a CDV; if it does, no one has been able to find it yet (including Zeckhausen racing, the guys that have been helping enthusiasts get rid of their CDV for a decade.)
I would say the pairing between this N55 and the 6MT is a very balanced equation. It truly is very similar to the previous 335i but with a bit more "precision." The turbo lag from the N54 has vanished and is now replaced with a low-end push from the rear that feels very linear and smooth straight away.
As a heads up; like many of you, I also could not find a 6MT 335i to test drive, so I went into this completely blind with only my past experience. Very glad and happy with my decision, I would have been bored and quite disappointed having it any other way